Spatial summation of pressure pain: effect of body region.

The characteristics of spatial summation of pressure pain are not clear. Pressure pain threshold (PPT) and perceived pressure pain intensity were measured in the hand, painfree back and myofascial trigger points (MTPs) in the back, using three different stimulus areas (0.5, 1 and 2 cm(2)). PPT decreased and perceived pain increased significantly with an increase in stimulation area in all the regions (e.g. PPT in the back, from 406+/-168 to 205+/-102kPa, P<0.0001). The magnitude of spatial summation of pressure pain was not significantly different between the regions. However, PPT in the back was significantly higher compared to the hand and MTPs (e.g. for 2 cm(2): mean of 205+/-102 vs 175+/-75 and 159+/-72kPa, P<0.01, respectively). Irrespective of body region, the quality of pain evoked with the large areas (1 and 2 cm(2)) was of pressure whereas in the small area (0.5 cm(2)) it was perceived as a prick. In conclusion, both PPT and perceived pressure pain intensity are subject to a considerable spatial summation in all the regions tested. The quality of pressure-evoked pain is probably determined by this spatial summation. Body region significantly affects the PPT level for a fixed stimulation area but not the magnitude of its spatial summation for areas up to 2 cm(2), which are probably within the receptive field of single spinal nociceptive neurons.